1. Field of the Disclosure
The invention pertains to evaluation methods for patients, and, in particular, to such methods of evaluating potential for pressure sores or discomfort of patients.
2. Description of the Related Art
In order to maximize compliance for continuous positive airway pressure (CPAP) therapy, for example, patient interface masks are designed to optimize comfort for the patient. Currently, patient comfort is assessed by return calls or follow up treatments after the patient has been on CPAP therapy for some time period.
It is generally believed that all patient interface masks generate some level of discomfort by applying pressure to the patient's face. This pressure can lead to minor red marks (e.g., a minimum level of discomfort) or open sores (e.g., a maximum discomfort). For example, it is believed that about 70% of the CPAP population gets some level of pressure sore.
Population variations add complexity to this problem. Individuals have widely varying sensitivities to mechanical pressure. Webster, J. G., “Prevention of Pressure Sores,” IOP publishing (1991), pp. 1-47, discloses pressure sores caused by stagnant pressure on the skin resulting from a clinical condition. Such pressure sores include, for example, bedsores (of a bedridden patient) and sores (of a wheelchair-bound patient). Reduced blood flow is the root cause of pressure sores and varies with factors such as: vascular disease state, muscular/fatty tissue physiology, age, gender, and many other factors.
Further complexity is added from the effects of shear force. Blood flow can be reduced by both normal and shear forces applied to the skin. Most conventional pressure measurement techniques (e.g., strain based pressure sensors, thin film pressure sensors, color indicating film) do not measure shear force.
The dermis of a patient is at risk from excessive strain from pressure. The various convoluted capillary tubes can easily be bent over (e.g., kinked) by shear force which results in the occlusion of blood flow. Normal stress pressure on the capillary tubes can also cause the restriction or occlusion of blood flow.
It is known that when mechanical stress is applied to the tissues of a person having one or more conditions relating to skin temperature, age, infection, body type, collagen formation, nutrition, and fibrinolytic activity, that it is likely that a pressure sore will result. The first stage of pressure sore development affects the epidermis and can involve a circumscribed reddened area that appears bruised with no break in skin integrity. Light finger pressure can cause blanching.